Many therapeutic agents, such as anthracyclines and vinca alkaloids, are especially effective for the treatment of cancers. However, these molecules are often characterized in vivo by an acute toxicity, especially a bone marrow and mucosal toxicity, as well as a chronic cardiac toxicity in the case of the anthracyclines and chronic neurological toxicity in the case of the vinca alkaloids. Similarly, methotrexate may be used for the treatment of inflammatory reactions, such as rheumatic diseases, but its high toxicity limits its applications. Development of more and safer specific antitumor agents is desirable for greater effectiveness against tumor cells and a decrease in the number and severity of the side effects of these products (toxicity, destruction of non-tumor cells, etc.). Development of more specific anti-inflammatory agents is also desirable.
In order to minimize toxicity problems, therapeutic agents are advantageously presented to patients in the form of prodrugs. Prodrugs are molecules capable of being converted to drugs (active therapeutic compounds) in vivo by certain chemical or enzymatic modifications of their structure. For purposes of reducing toxicity, this conversion should be confined to the site of action or target tissue rather than the circulatory system or non-target tissue. Prodrugs are often characterized by a low stability in blood and serum, however. This is due to the presence of enzymes in blood and serum that degrade, and consequently may activate, the prodrugs before the prodrugs can reach the desired sites within the patient's body.
A desirable class of prodrugs that overcomes such problems has been disclosed in Patent Cooperation Treaty International Publication No. WO 96/05863 and in U.S. Pat. No. 5,962,216, both incorporated herein by reference. Further useful prodrug compounds and methods of making such prodrugs are desirable, however, as are methods of making the prodrugs.
Prodrugs that display a high specificity of action, a reduced toxicity, and an improved stability in blood especially relative to prodrugs of similar structure (especially the closest structure) that have existed in the public domain are particularly desirable.